A variety of methods are used in the semiconductor manufacturing industry to deposit materials onto surfaces. For example, one widely used method is chemical vapor deposition (“CVD”), in which atoms or molecules contained in a vapor are deposited onto a surface and built up to form a film. Multiple deposition steps can be sequenced to produce devices with several layers. In such multi-layer processes, it is generally desired to maintain planarity from level to level during the deposition processes. Poor planarity, particularly during early deposition steps, tends to be amplified through higher levels of device fabrication. Poor planarity can create problems for photolithographic steppers, risking misalignment in precise masking steps.
Silicon germanium (SiGe) films, which are used in a wide variety of semiconductor applications, can be deposited using a CVD process in which silicon and germanium are delivered to a surface where they react and form a film. SiGe films formed using CVD processes can have various morphologies, including single crystalline, amorphous, and polycrystalline. In epitaxial deposition of a SiGe film, the initial crystalline structure and morphology of the deposited film follows the crystalline information of the underlying material onto which the epitaxial deposition occurs. Additionally, SiGe films can be formed in a selective deposition process or in a blanket deposition process. In a selective deposition, the film is deposited over certain areas of a substrate, whereas in a blanket deposition, the film is deposited over substantially the entire substrate.